(1) Field of the invention
The present invention relates to a system and method for communicating between data processing stations such as a master station (i.e. a diagnostic device) and various substations (i.e. electronic control units installed in a vehicle) to diagnose problems in electronic control units (ECU's) controlling vehicle components such as, for example, a vehicular engine.
(2) Description of the background art
Along with recent technological developments in semiconductor devices, essential vehicle components have rapidly become electronically controlled and a multiple number of microprocessors have found their way into most vehicles to be used as electronic control units (ECUs) for such as engine control, etc.
Although such electronically controlled systems achieve high-performance and make for more comfortable vehicles, diagnosis of malfunctions in the control units is very complex. This is because it is often difficult to trace the causal relationship between a generated phonomenon and its cause, a high degree of technological knowledge is needed to analyze such causal relationships and such minute electrical signals are susceptible to external noises, as well as intermittent discontinuities.
Therefore, although many electronic control units add self-diagnostic functions, however, since such diagnoses are carried out on an on-board basis, and the microprocessors of most ECU's are rather small, their processing capabilities are restricted.
In response to the above, a master station constituting an off-board diagnostic device which carries out off-board diagnoses and which is capable of making precise, high-quality diagnosis has been developed.
In a case where each electronic control unit installed in the vehicle is diagnosed from the master station, the master station selects a desired electronic control unit from among the plurality of electronic control units installed in the vehicle, transmits a diagnostic control command to the selected electronic control unit, and receives return data from the selected electronic control unit in response to the diagnostic control command.
In such a data communication as described above, the master station initially transmits an initializing command to set each electronic control unit via a communication circuit located between the master station and the plurality of electronic control units to place the ECU's in a receive standby state for a system call command which will select the desired electronic control unit from among the plurality of electronic control units.
Upon transmission of the command through the communication circuit setting each electronic control unit in the receive standby state for a system call command, the master station transmits the system call command to select only a desired electronic control unit so that a data link from the master station to the selected electronic control unit is established.
When the data link is established between the master station and the selected electronic control unit, the master station transmits a control command such as a parameter set command, the control command being issued to cause the selected electronic control unit to execute a desired control operation. The control command is followed, at a predetermined time interval, by two information bytes which are successively transmitted subsequent the control command. The two information bytes also have a predetermined time interval provided therebetween. The item to be controlled is set by the first information byte and the controlled variable thereof is set by the subsequent second information byte. Then, the master station monitors the response characteristic of the vehicle system controlled by the selected ECU to compare that the vehicle response correlates with the ECU parameter specified by the control command. Diagnosis of malfunction in the electronic control unit is carried out in this way.
However, in communication between the master station and an electronic control unit, after the master station transmits the initialize command to each electronic control unit via the communication circuit, and selects a particular ECU for establishing a data link the following problems can occur; due to the limited combinations of 1 and 0 which are allowed within a single byte, and the large number of control parameters utilized by the master station, it is possible that the first information byte transmitted after a control command may contain the same bit combination as the initialize command and the second information byte may contain the same bit combination as a system call command to an electronic control unit other than the selected electronic control unit, the other non-selected electronic control unit would then erroneously respond to the false initialize command constituted by the first information byte and system call command constituted by the second information byte.
In more detail, a normal echoback signal from the selected electronic control unit would be destroyed due to the new echoback signal from the other electronic control unit responding to the erroneous system call command. Consequently, normal communication between the master station and the selected electronic control unit will not be achieved.